The effect of sodium octadecyl sulfate on the electrokinetic potential of metal oxides

Dispersions of hematite, titania, and alumina containing sodium octadecyl sulfate have been studied. Increasing concentrations of the surfactant induced a shift in the IEP to low pH, and at sufficiently high surfactant concentrations, the zeta potential assumed negative values over the entire pH range. The zeta potential vs. pH curves obtained in sodium octadecyl sulfate - metal oxide systems belong to the type I electrokinetic curves described in our previous study, that is, these curves do not show a maximum at nearly neutral pH. Our results confirm that in long-chained sodium alkyl sulfates type I electrokinetic curves are observed, as opposed to the type II electrokinetic curves (with a maximum at nearly neutral pH), which are observed in short-chained sodium alkyl sulfates.